EDM's are presently commonly used for making precise cuts and shaping various electrically conductive materials or workpieces. The cutting and shaping of the workpiece is accomplished by precisely placing the electrode close to the workpiece and placing the workpiece and electrode at different electrical potentials and thereby causing electrical sparks to occur between the electrode and the workpiece. The sparks erode the workpiece in a desired manner and simultaneously consume the electrode.
For boring holes and other shapes into a workpiece, an electrode such as a rod-shaped, tube-shaped, etc., member is accurately lowered onto the workpiece thereby causing electro-erosion therebetween and forming a bore or hole in the workpiece which is a mirror image of the electrode. Because the electrode is also eroded during the cutting process, it must continuously be replenished for achieving the desired depth.
For cutting through a workpiece, EDM's typically utilize a wire electrode which is wound around and travels between two turning spools. Wire guides are used to accurately locate the moving wire electrode with respect to the workpiece so that sparks occurring between the wire and workpiece effectively and accurately cut through the workpiece. Here, the wire electrode is not totally consumed but, rather, is continuously being replenished as its exterior surface is spark eroded.
In welding apparatus, a wire electrode is again used and is guided through a guiding device and onto the workpiece. A bushing is often used for guiding the wire. The bushing may also be used as a current transfer element. Various gases such as metal inert gases can be used and are typically provided around the juncture between the workpiece and electrode for enhancing the welding process. The heat generated due to the different electrical potential between the workpiece and electrode deposits the electrode as it is fed toward the workpiece through the guiding device.
Wire electrode EDM's generally require substantially more accurate guidance of the wire than welding apparatus. In this regard, early wire EDM guide systems used a V-shaped component made of ruby or sapphire for accurately guiding the moving wire electrode. Unfortunately, V-shaped guides cause difficulties when generating taper/conical cuts, since the angular pivot point of the wire shifts with the conical direction.
More recently, orifice-shaped or type guides have been employed for guiding the moving wire electrode. The orifice is typically manufactured to be slightly larger than the wire electrode diameter. The wire electrode is passed through an upper guide and a lower guide which are each selectively movable with respect to each other and the workpiece. Accordingly, the wire electrode is exposed to the workpiece at any desired angle and cutting direction. The orifices are typically toroid-shaped and are preferably made through diamond, although carbide, ceramic, ruby and sapphire can be used as well.
Although orifice-type guides generally provide a sufficient means for guiding the wire electrode, they too have substantial shortcomings. So as to provide a sufficiently lasting orifice guide, typically a material with extreme hardness such as diamond is required. Although industrial diamonds themselves are not expensive, geometrically consistent machining and polishing of complex toroidal shapes through the diamonds for forming the orifice is substantially time-consuming and expensive. Additionally, the diamond orifice is typically located in a diamond wafer which is then captivated in a metal mount. Unfortunately, the metal mount is itself subject to erosion which eventually can expose the diamond wafer or disk and exposing an undesirable ledge. Exposed ledges of this character can hamper wire threading and can render automatic threading operations impractical.
Additional difficulties with respect to orifice-type guides have also been encountered due to the frictional forces and extreme heating of the electrode. Electrical cutting current is necessarily transferred through the electrode which causes resistive heating. This heating limits efficiency of the process to the point at which the wire can be cooled. Additionally, because the wire diameter is substantially the same as that of the orifice, even though a dielectric fluid is provided thereat, the fluid cannot easily travel through the orifice for cooling the walls thereof. Indeed, so as to achieve higher accuracies, the wire electrode is the same diameter as that of the orifice and effectively prevents dielectric fluid flow therethrough. This restriction can cause additional problems due to electro eroded particulates and other debris accumulating near or at the orifice.
Accordingly, a need exists for an electrode guide that solves the problems and shortcomings associated with prior electrode guiding devices and which is generally inexpensive to manufacture and yet has a sufficiently long life and is capable of accurately locating the electrode.